Wireless electrocardiogram (ECG) monitors, which are placed on a patient to permit the remote monitoring of cardiac rhythm are known e.g. from U.S. Pat. No. 3,943,918. It is also known to provide wireless heart rate monitors which are held against the patient by a chest strap. Not only do such devices tend to be heavy and bulky but the degree of contact with the skin is generally poor and prone to motion artefacts. Moreover the need for a chest strap to be fitted around the subject means that they may not be suitable in trauma situations are where the subject is physically injured or disabled. The Applicant has devised an improved arrangement which aims to alleviate at least some of the shortcomings of known devices.